Sealed condition inspecting device

ABSTRACT

An object of the present invention is to provide a seal condition inspection apparatus capable of reliably inspecting seal condition. The seal condition inspection apparatus includes an electrically-variable-quantity detecting section for detecting an electrically variable quantity at a portion (F) to be inspected for seal condition; a seal condition indicator value calculation processing means for calculating, on the basis of the electrically variable quantity, a seal condition indicator value indicative of seal condition of the portion (F) to be inspected; and a seal condition judgment processing means for judging from the seal condition indicator value whether seal condition is good or defective. In this case, the seal condition indicator value of the portion (F) to be inspected is calculated on the basis of the electrically variable value of the portion (F) to be inspected, and whether seal condition is good or defective is judged on the basis of the seal condition indicator value. Therefore, occurrence of a seal defect can be judged without involvement of an operator&#39;s subjectivity. As a result, seal condition can be reliably inspected.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Phase Application (35 USC 371) ofPCT/JP02/13605 and claims priority of Japanese Application No.2001-397218, filed Dec. 27, 2001.

1. Technical Field

The present invention relates to a seal condition inspection apparatus.

2. Background Art

Conventionally, in production of packaging containers that containliquid food such as milk or soft drink, a Web-like packaging material, acarton-blank-like packaging material, or the like is formed intopackaging containers by means of sealing at predetermined positionsthrough heat sealing, ultrasonic sealing, or a like method. For example,when a web-like packaging material is used, in a filling apparatus, theweb-like packaging material is formed into a tubular shape; the tubularpackaging material is sealed in the longitudinal direction by means of afirst sealing device; while being filled with liquid food, thelongitudinally sealed tubular packaging material is sealed in thelateral direction and cut at predetermined intervals by means of asecond sealing device to thereby yield a pillow-like prototypecontainer; and the prototype container is formed into a final packagingcontainer.

Meanwhile, in order to seal the above-mentioned packaging material, thepackaging material is gripped from opposite sides at a predeterminedgripping pressure, and resin on the surfaces of the packaging materialis melted through application of heat, thereby fusing the surfaces ofthe packaging material together. However, for example, when the grippingpressure is too high, molten resin is squeezed from a seal portion. As aresult, the amount of resin remaining in the seal portion becomesinsufficient, potentially resulting in occurrence of a seal defect.Occurrence of a seal defect causes leakage of liquid food from apackaging container or entry of air into the packaging container, with aresultant deterioration in the quality of liquid food.

Thus, an operator empties a completed packaging container of liquidfood, cuts the empty packaging container open, and visually inspects alongitudinally sealed portion, or a first seal portion, as well as alaterally sealed portion, or a second seal portion, for seal conditionfrom the inside of the packaging container.

However, the above-mentioned conventional method for inspecting sealcondition involves an operator's subjective judgment about occurrence ofa defect, thus failing to reliably inspect seal condition.

An object of the present invention is to solve the above-mentionedproblem in the conventional method for inspecting seal condition and toprovide a seal condition inspection apparatus capable of reliablyinspecting seal condition.

DISCLOSURE OF THE INVENTION

To achieve the above object, a seal condition inspection apparatus ofthe present invention comprises an electrically-variable-quantitydetecting section for detecting an electrically variable quantity at aportion to be inspected for seal condition; seal condition indicatorvalue calculation processing means for calculating, on the basis of theelectrically variable quantity, a seal condition indicator valueindicative of seal condition of the portion to be inspected; and sealcondition judgment processing means for judging from the seal conditionindicator value whether seal condition is good or defective.

In this case, the seal condition indicator value of the portion to beinspected is calculated on the basis of the electrically variable valueof the portion to be inspected, and whether seal condition is good ordefective is judged on the basis of the seal condition indicator value.

Therefore, occurrence of a seal defect can be judged without involvementof an operator's subjectivity. As a result, seal condition can bereliably inspected.

In another seal condition inspection apparatus of the present invention,the seal condition indicator value is the capacitance of the portion tobe inspected.

In a further seal condition inspection apparatus of the presentinvention, the seal condition indicator value is the loss factor of theportion to be inspected.

In still another seal condition inspection apparatus of the presentinvention, the seal condition indicator value is the capacitance andloss factor of the portion to be inspected.

In a still further seal condition inspection apparatus of the presentinvention, the electrically-variable quantity is voltage applied to theportion to be inspected and current flowing through the portion to beinspected.

Yet another seal condition inspection apparatus of the present inventionfurther comprises a phase separating section for detecting, on the basisof current flowing through the portion to be inspected, an in-phasecomponent having the same phase as that of voltage applied to theportion to be inspected, and an out-of-phase component having a phasedifferent from that of voltage applied to the portion to be inspected.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view showing a main portion of a filling apparatusin an embodiment of the present invention;

FIG. 2 is a schematic view of a seal condition inspection apparatusaccording to the embodiment of the present invention;

FIG. 3 is a view showing the principle of a method for inspecting sealcondition according to the embodiment of the present invention;

FIG. 4 is a block diagram of the seal condition inspection apparatusaccording to the embodiment of the present invention; and

FIG. 5 is a waveform chart showing the operation of the seal conditioninspection apparatus according to the embodiment of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will next be described in detailwith reference to the drawings. The present embodiment will be describedwhile mentioning a seal condition inspection apparatus for detecting theseal condition of a brick-like packaging container. However, the presentinvention can be applied to a seal condition inspection apparatus fordetecting the seal condition of another-type of packaging container.

FIG. 1 is a schematic view showing a main portion of a filling apparatusaccording to the embodiment of the present invention.

A web-like packaging material produced by an unillustratedpackaging-material production machine is set on an unillustrateddelivery unit of a filling apparatus, delivered by means of the deliveryunit, and caused to travel through the filling apparatus by means of afeeder.

While the packaging material is traveling, an unillustrated hole ispunched in the packaging material, and an unillustrated inner tape andan unillustrated pull tab are affixed to the packaging material in sucha manner as to cover the punched hole. Subsequently, the packagingmaterial is caused to travel vertically. While being guided by means ofa plurality of unillustrated forming rings disposed along the travelingdirection, the vertically traveling packaging material is formed into atubular shape. The tubular packaging material is sealed in thelongitudinal direction by means of an unillustrated first sealing deviceto thereby become a packaging-material tube 11.

Subsequently, liquid food is supplied from above into thepackaging-material tube 11 via an unillustrated filling pipe. Next,first and second sealing jaw devices 44 and 45, which constitute asecond sealing device, grip the packaging-material tube 11 from oppositesides. The packaging-material tube 11 is laterally sealed atpredetermined longitudinal intervals and is formed into a pillow-likeprototype container 18 through deformation effected by means of formingflaps 46 and 47.

Each of the first and second sealing jaw devices 44 and 45 has a cuttingjaw 51 and a heat seal jaw 52. In this case, while thepackaging-material tube 11 is fed downward in an intermittent manner,the first and second sealing jaw devices 44 and 45 of the same structureare alternatingly operated such that their operating cycles are shiftedfrom each other by half cycle, thereby enhancing the processing speed ofthe filling apparatus.

The cutting jaw 51 has a cutting bar 53 provided at the front end (atthe right-hand end in FIG. 1); the heat seal jaw 52 has a seal block (aninductor insulator) 54 provided at the front end (at the left-hand endin FIG. 1); and the seal block 54 has two inductors 55. The cutting jaw51 and the heat seal jaw 52 are caused to advance so as to grip thepackaging-material tube 11 from opposite sides by means of the cuttingbar 53 and the seal block 54, whereby the facing surfaces of thepackaging-material tube 11 are brought in contact with each other. Thethus-gripped packaging-material tube 11 undergoes lateral sealing at thegripped portion, thereby forming a second seal portion S including twoseal lines.

A laterally extending flat cutter knife 56 is provided at the center ofthe cutting jaw 51 in such a manner that the cutter knife 56 can advanceand retract (can move rightward and leftward in FIG. 1). When the cutterknife 56 is advanced. (moved rightward in FIG. 1), the cutter knife 56cuts the second seal portion S at an intermediate position between thetwo seal lines.

A cylinder 57 is disposed at the rear end (the left-hand end in FIG. 1)of the cutter knife 56 so as to advance and retreat the cutter knife 56through supply of compressed air or the like to and release the samefrom the cylinder 57.

A pair of forming flaps 46 and 47 are pivotably attached to the cuttingjaw 51 and the heat seal jaw 52, respectively in such a manner as tosurround and guide the packaging-material tube 11, and are adapted toform the packaging-material tube 11 into a brick-like shape whileguiding the packaging-material tube 11.

In FIG. 1, the first sealing jaw device 44 is at the sealing-cuttingstart position. At the sealing-cutting start position, the first sealingjaw device 44 causes the cutting jaw 51 and the heat seal jaw 52 toadvance so as to grip the packaging-material 11 from opposite sides,whereby the facing surfaces of the packaging-material 11 are broughtinto contact with each other. Then, while gripping thepackaging-material tube 11, the first sealing jaw device 44 movesdownward. During the downward movement, the second seal portion S isformed, thereby forming the prototype container 18.

In FIG. 1, the second sealing jaw device 45 is at the sealing-cuttingend position. Immediately before the second sealing jaw device 45reaches the sealing-cutting end position, the cutter knife 56 of thesecond sealing jaw device 45 is caused to advance and cut the secondseal portion S at an intermediate position between the two seal lines,thereby separating the prototype container 18.

When the second seal portion S is cut at an intermediate positionbetween the two seal lines, the cutting jaw 51 and the heat seal jaw 52of the second sealing jaw device 45 are caused to retreat and then moveupward in a gyrating manner to the sealing-cutting start position. When,at the sealing-cutting start position, the second sealing jaw device 45begins to cause the cutting jaw 51 and the heat seal jaw 52 to advance,the cutter knife 56 of the first sealing jaw device 44 advances and cutsthe second seal portion S at an intermediate position between the twoseal lines, thereby separating the prototype container 18.

Notably, each of the first and second sealing jaw devices 44 and 45 hasan unillustrated cylinder mechanism. At the sealing-cutting startposition, compressed air or the like is supplied to the cylindermechanism in order to draw the cutting jaw 51 and the heat seal jaw 52to each other, thereby increasing the gripping pressure for sealing.

Subsequently, each prototype container 18 undergoes folding alongpreviously formed folding lines so as to be formed into a predeterminedshape, thereby assuming the form of a brick-like packaging containerwhich contains a predetermined amount of liquid food.

Meanwhile, the packaging material assumes a laminate structure composedof, for example, a first resin layer formed from resin such aspolyethylene and serving as an inside layer, an aluminum foil layerserving as a barrier layer, a paper substrate, and a second resin layerformed from resin such as polyethylene and serving as an outside layer,which are arranged in this order from the inside toward the outside whena packaging container is formed from the packaging material. Notably,instead of the aluminum foil layer, a resin layer formed from resin suchas polyester may be used as the barrier layer. Reference numeral 38denotes a guide roller for guiding the packaging-material tube 11.

In order to seal the packaging material, the packaging material isgripped from opposite sides at a predetermined gripping pressure bymeans of the cutting jaw 51 and the heat seal jaw 52 and is exposed toheat or ultrasonic vibration, whereby the surfaces of the packagingmaterial are fused together through melting of the first and secondresin layers. However, for example, when the gripping pressure is toohigh, molten resin is squeezed from the second seal portion S. As aresult, the amount of resin remaining in the second seal portion Sbecomes insufficient, potentially resulting in occurrence of a sealdefect. Occurrence of a seal defect causes leakage of liquid food from apackaging container or entry of air into the packaging container, with aresultant deterioration in the quality of liquid food.

Thus, an operator empties a completed packaging container of liquidfood, cuts the empty packaging container open, and inspects from theinside of the packaging container the first seal portion, the secondseal portion S, and the like for seal condition. However, visualinspection for seal condition involves an operator's subjective judgmentabout occurrence of a defect, thus failing to reliably inspect sealcondition.

Next will be described a seal condition inspection apparatus capable ofelectrically inspecting the seal portions for seal condition. Notably,since the first seal portion assumes the same structure as that of thesecond seal portion S, description in relation to the first seal portionis omitted.

FIG. 2 is a schematic view of a seal condition inspection apparatusaccording to the embodiment of the present invention; FIG. 3 is a viewshowing the principle of a method for inspecting seal conditionaccording to the embodiment of the present invention; FIG. 4 is a blockdiagram of the seal condition inspection apparatus according to theembodiment of the present invention; and FIG. 5 is a waveform chartshowing the operation of the seal condition inspection apparatusaccording to the embodiment of the present invention.

In the drawings, reference symbol S denotes a second seal portion, andreference numeral 17 denotes a packaging material. The packagingmaterial 17 includes a first resin layer 12, an aluminum foil layer 13,a paper substrate 14, and a second resin layer 15. When thepackaging-material tube 11 (FIG. 1) is to be laterally sealed, thecutting jaw 51 and the heat seal jaw 52 are caused to advance so as togrip the packaging-material tube 11 from opposite sides, followed byapplication of heat or ultrasonic vibration. At this time, mutuallyfacing portions of the first resin layer 12 are brought in contact witheach other, and resin, for example, polyethylene used to form the firstresin layer 12 melts, thereby forming a fused portion 16.

At the second seal portion S, mutually facing two portions of thepackaging material 17 are layered and joined together by the fusedportion 16. Since the first and second resin layers 12 and 15 and thelike are formed from dielectric materials, the second seal portion Sfunctions as a capacitor 31. When the barrier layer is formed from resinsuch as polyester, the barrier layer is formed from a dielectricmaterial. An unillustrated bonding layer is formed from adhesiveintervenes between the aluminum foil layer 13 and the paper substrate14. The bonding layer is formed from a dielectric material.

The second seal portion S serves as a portion F to be inspected for sealcondition. The seal condition inspection apparatus inspects the sealcondition of the portion F to be inspected, on the basis of capacitanceof the portion F as measured when AC current is supplied to the portionF. The capacitance serves as a first seal condition indicator valueindicative of the seal condition of the portion F to be inspected.

In order to carry out the above inspection, the seal conditioninspection apparatus includes two electrodes 21 and 22; a power supplyunit (AC) 23, which serves as an applied-voltage generating section forgenerating AC voltage to be applied to the portion F to be inspected; acurrent sensor 24, which serves as an electrically-variable-quantitydetecting section for detecting an electrically variable quantity at theportion F to be inspected; a detection processing section 25 forcarrying out processing for reading voltage which is generated by thepower supply unit 23, and current which is detected by the currentsensor 24; a control section 26 including a CPU for controlling theentire seal condition inspection apparatus; a display unit 27 includingindicator lamps and a display; an operation section 28 for carrying outvarious operations; and a storage unit 29 for recording predetermineddata. The current sensor 24 serves as a current detecting section anddetects AC current which flows through the portion F to be inspected, asthe above-mentioned electrically variable quantity. According to thepresent embodiment, the detection processing section 25 directly reads asignal indicative of voltage generated by the power supply unit 23 tothereby detect the voltage. However, an unillustrated voltage sensorwhich serves as a voltage detecting section may be disposed such thatthe detection processing section 25 reads voltage which is detected bythe voltage sensor.

The electrodes 21 and 22 are each formed from a plate of an electricallyconductive material having a predetermined area and are disposed inopposition to each other. When the portion F is inspected for sealcondition, the electrodes 21 and 22 are pressed against the portion F tobe inspected, at a predetermined pressure such that the portion F to beinspected is sandwiched therebetween. Thus, at least one of theelectrodes 21 and 22 is disposed to be advancable and retractablerelative to the other (vertically movable in FIG. 2) and can be moved bymeans of an unillustrated moving mechanism. The electrodes 21 and 22 areconnected to each other via the power supply unit 23 and the currentsensor 24 and are adapted to apply to the portion F to be inspected apredetermined voltage which the power supply unit 23 generates.

Voltage to be applied to the portion F to be inspected is set accordingto properties of the packaging material 17; for example, according tomaterials and thicknesses of the first resin layer 12, aluminum foillayer 13, paper substrate 14, and second resin layer 15. When voltage isapplied to the portion F to be inspected, the power supply unit 23 andthe portion F to be inspected form an equivalent circuit as shown inFIG. 3. The portion F to be inspected is represented by a parallelcircuit in which a capacitor 31 having a capacitance Cp and an internalresistance 32 having a resistance Rp are connected in parallel. When thecapacitor 31 and the internal resistance 32 are used to represent anequivalent circuit, whether the capacitor 31 and the internal resistance32 are connected in series or in parallel depends on the impedance ofeach of the capacitor 31 and the internal resistance 32. As in the caseof the second seal portion S, when the impedance of the internalresistance 32 is very large in relation to the impedance of thecapacitor 31, they are generally connected in parallel.

When s represents the area of each of the electrodes 21 and 22, drepresents the thickness of the portion F to be inspected; i.e., thedistance between load electrodes (the distance between the electrodes 21and 22), and ε represents dielectric constant, the above-mentionedcapacitance Cp is expressed byCp=∈·s/d

In this case, the dielectric constant ∈ of the portion F to be inspectedvaries depending on the attributes of the packaging material 17; forexample, the material and thickness of the first resin layer 12,aluminum foil layer 13, paper substrate 14, and second resin layer 15. Avariation in the dielectric constant ∈ leads to a variation in thecapacitance Cp at the portion F to be inspected. Particularly, thedielectric constant ∈ of the portion F to be inspected varies greatlydepending on the material and thickness of layers formed from adielectric material, such as the first and second resin layers 12 and 15and the paper substrate 14. A great variation in the dielectric constant∈ at the portion F to be inspected leads to a great variation in thecapacitance Cp at the portion F to be inspected.

Also, the distance d between load electrodes varies depending on sealingconditions for the second seal portion S; for example, the meltingtemperature of resin and a gripping pressure exerted by the cutting jaw51 and the heat seal jaw 52. A variation in the distance d between loadelectrodes leads to a variation in the capacitance Cp at the portion Fto be inspected. For example, the higher the melting temperature or,gripping pressure, the more molten resin is squeezed sideward at thesecond seal portion S. Thus, the thickness of the fused portion 16decreases accordingly. Therefore, the distance d between load electrodesdecreases, and thus the capacitance Cp at the portion F to be inspectedincreases accordingly.

The degree of fusion of the fused portion 16 varies depending on amethod for sealing the second seal portion S; i.e., a sealing method. Avariation in the degree of fusion leads to a variation in thecapacitance Cp at the portion F to be inspected. As for a method forsealing the second seal portion S, a block seal method and a fusion sealmethod are available. For example, when the block seal method isemployed, fusion of resin of the first resin layer 12 is not involved.Therefore, the fused portion 16 is hardly formed, and the mutuallyfacing portions of the first resin layer 12 are merely affixed to eachother. The amount of resin at the second seal portion S does notdecrease; thus, the distance d between load electrodes remain unchanged,and the capacitance Cp at the portion F to be inspected remainsunchanged.

By contrast, when the fusion seal method is employed, resin of the firstresin layer 12 is melted, thereby joining the mutually facing portionsof the packaging material 17 together through fusion. In this case, theamount of resin at the second seal portion S decreases; thus, thedistance d between load electrodes decreases, and the capacitance Cp atthe portion F to be inspected increases accordingly.

Furthermore, the area of contact with the electrodes 21 and 22 variesdepending on seal structure such as a seal length represented by thelength of a seal line and a seal width represented by the width of theseal line in sealing the second seal portion S by means of the secondsealing device. A variation in the area of contact with the electrodes21 and 22 leads to a substantial variation in area s of the electrodes21 and 22, and thus the capacitance Cp at the portion F to be inspectedvaries accordingly.

As described above, the capacitance Cp at the portion F to be inspecteddepends on the attributes of the packaging material 17, the sealingconditions of a sealing device, a sealing method, the structure of thesealing device, and the like. Thus, the capacitance Cp can be used as anindicator of seal condition in relation to judgment of whether sealcondition is good or defective.

Thus, voltage Vs generated in the power supply unit 23 is set accordingto the attributes of the packaging material 17, the sealing conditionsof the sealing device, a sealing method, the structure of a sealingdevice, and the like.

When, in the equivalent circuit: shown in FIG. 3, Icp and Irp representcurrent which flows through the capacitor 31 and the internal resistance32, respectively, at the time of the power supply unit 23 applyingvoltage Vs of frequency f to the portion F to be inspected, impedance Zcof the capacitor 31 is expressed byZc=1/(2π·f·Cp)  (1)Therefore, the current Icp is expressed by

$\begin{matrix}\begin{matrix}{{Icp} = {{Vs}/{Zc}}} \\{= {2{\pi \cdot f \cdot {Cp} \cdot {Vs}}}}\end{matrix} & (2)\end{matrix}$Then, the capacitance Cp is expressed byCp=Icp/(2π·f·Vs)  (3)Notably, the voltage Vs serves as applied voltage; the current Icpserves as first inspected-portion current; and the current Irp serves assecond inspected-portion current.

Loss factor D, which serves as a second seal condition indicator valueindicative of seal condition of the portion F to be inspected, can beexpressed byD=1/(2π·f·Cp·Rp)  (4)Thus, the resistance Rp of the internal resistance 32 is expressed byRp=1/(2π·f·Cp·D)  (5)

The current Irp flowing through the internal resistance 32 is expressedbyIrp=Vs/Rp  (6)Substituting Eq. (5) into Eq. (6) givesIrp=(2π·f·Cp·D)·Vs  (7)Substituting Eq. (3) into Eq. (7) givesIrp=Icp·DThus, the loss factor D is expressed byD=Irp/Icp  (8)That is, the loss factor D can be represented by the ratio of thecurrent Icp to the current Irp and thus can be used as an indicator ofseal condition in relation to judgment of whether seal condition is goodor defective.

The current It flowing through the portion F to be inspected isexpressed byIt=Icp+Irp  (9)

Since the capacitance Cp can be calculated by Eq. (3), and the lossfactor D can be calculated by Eq. (8), the capacitance Cp and the lossfactor D can be calculated when the voltage Vs and the currents Icp andIrp are known.

In this case, the capacitor 31 and the internal resistance 32 areequivalently present at the portion F to be inspected and cannot bedetected from the outside of the portion F to be inspected.

Thus, on the basis of the current It detected by the current sensor 24,the current Icp and the current Irp are calculated. In this case, asshown in FIG. 5, since the current Irp is a component which flowsthrough the internal resistance 32, the current Irp has the same phaseas that of the voltage Vs applied to the portion F to be inspected.Since the current Icp is a component which flows through the capacitor31, the phase of the current Icp differs 90° from that of the voltage Vs(leads by 90°). Therefore, the current It is sent (in actuality, thecurrent It is converted to voltage Vt, and the voltage Vt is sent) to aphase separation circuit for separating the current It into the currentIcp and the current Irp.

Thus, the detection processing section 25 includes an A/D converter 61which reads the voltage Vs of the power supply unit 23 and performsanalog-to-digital conversion on the read the voltage Vs; acurrent-to-voltage converter 62 which reads the current. It and convertsthe read It to voltage Vt; an in-phase component detecting section 33for detecting an in-phase component of the voltage Vt whose phase is thesame as that of the voltage Vs; an out-of-phase component detectingsection 34 for detecting an out-of-phase component of the voltage Vtwhose phase differs from that of the voltage Vs; an A/D converter 35which reads the in-phase component detected by the in-phase componentdetecting section 33 and performs analog-to-digital conversion on theread in-phase component; and an A/D converter 36 which reads theout-of-phase component detected by the out-of-phase component detectingsection 34 and performs analog-to-digital conversion on the readout-of-phase component. Notably, the in-phase component detectingsection 33 and the out-of-phase component detecting section 34constitute the phase separation circuit, which serves as the phaseseparating section.

Thus, the voltage Vs in the form of a digital signal can be output fromthe A/D converter 61; the current Irp in the form of a digital signalcan be output from the A/D converter 35; and the current Icp in the formof a digital signal can be output from the A/D converter 36. The outputvoltage Vs and currents Icp and Irp are sent to the control section 26.Notably, the A/D converter 61 serves as the applied-voltage detectingsection; the out-of-phase detecting section 34 and the A/D converter 36constitute the first inspected-portion current detecting section; andthe in-phase detecting section 33 and the A/D converter 35 constitutethe second inspected-portion current detecting section.

The control section 26 reads the frequency f set in the power supplyunit 23, the voltage Vs, and the currents Icp and Irp. Subsequently,unillustrated capacitance calculation processing means of the controlsection 26 performs capacitance calculation processing in which thecapacitance Cp is calculated by Eq. (3). Unillustrated loss factorcalculation processing means of the control section 26 performs lossfactor calculation processing in which the loss factor D is calculatedby Eq. (8). Notably, the capacitance calculation processing means andthe loss factor calculation processing means constitute the sealcondition indicator value calculation processing means. The sealcondition indicator value calculation processing means performs sealcondition indicator value calculation processing in which thecapacitance Cp and the loss factor D are calculated.

The storage unit 29 retains, in the form of a table, referencecapacitors Cpref and reference loss factors Dref which are calculatedbeforehand on the basis of attributes of the packaging material 17,sealing conditions and methods of sealing devices, and structures ofsealing devices, in such a manner that a reference capacitor Cpref and areference loss factor Dref are provided for each of combinations amongtypes of the packaging material 17, sealing conditions, sealing methods,and sealing devices.

Unillustrated first seal condition judgment processing means of thecontrol section 26 performs first seal condition judgment processing inwhich the first seal condition judgment processing means references theabove-mentioned table, compares a reference capacitance Cpref and thecapacitance Cp calculated by the capacitance calculation processingmeans, and judges whether or not a deviation ΔCp as calculated below isequal to or less than a threshold value Cpth.ΔCp=|Cp−Cpref|

When the deviation ΔCp is equal to or less than the threshold valueCpth, the first seal condition judgment processing means judges thatseal condition is good. When the deviation ΔCp is greater than thethreshold value Cpth, the first seal condition judgment processing meansjudges that seal condition is defective. In this manner, the first sealcondition judgment processing means can judge whether seal condition isgood or defective.

Unillustrated second seal condition judgment processing means of thecontrol section 26 performs second seal condition judgment processing inwhich the second seal condition judgment processing means references theabove-mentioned table, compares a reference loss factor Dref and theloss factor D calculated by the loss factor calculation processingmeans, and judges whether or not a deviation ΔD as calculated below isequal to or less than a threshold value Dth.ΔD=|D−Dref|

When the deviation ΔD is equal to or less than the threshold value Dth,the second seal condition judgment processing means judges that sealcondition is good. When the deviation ΔD is greater than the thresholdvalue Dth, the second seal condition judgment processing means judgesthat seal condition is defective. In this manner, the second sealcondition judgment processing means can judge whether seal condition isgood or defective.

As described above, on the basis of the current It which flows throughthe portion F to be inspected when the voltage Vs is applied to theportion F to be inspected, a judgment is made as to whether sealcondition is good or defective. Thus, occurrence of a seal defect can bejudged without involvement of an operator's subjectivity, whereby sealcondition can be reliably inspected.

In the present embodiment, the judgement as to whether seal condition isgood or defective is performed in each of the first seal conditionjudgment processing and the second seal condition judgment processing.However, the judgement as to whether seal condition is good or defectivemay be performed on the basis of processing results of the first sealcondition judgment processing and the second seal condition judgmentprocessing.

The present invention is not limited to the above-described embodiment.Numerous modifications and variations of the present invention arepossible in light of the spirit of the present invention, and they arenot excluded from the scope of the present invention.

INDUSTRIAL APPLICABILITY

The present invention can be applied to a seal condition inspectionapparatus for inspecting a packaging container for seal condition.

1. A seal condition inspection apparatus for inspecting a seal betweentwo superimposed portions of a packaging material, the apparatuscomprising: a pair of opposing electrodes spaced apart a distance d anddisposed on opposing sides of a seal portion for pressing, with apredetermined pressure, the seal therebetween; a power supply unit,through which the electrodes are connected, for passing a currentthrough a portion of the seal between the electrodes; electricallyvariable-quantity detection means for detecting an electrically variablequantity of the seal at a portion between the opposing electrodes, saidvariable quantity varying as a function of distance d, to be inspectedfor seal condition; seal condition indicator value calculationprocessing means for calculating, on the basis of the detectedelectrically variable quantity, a seal condition indicator valueindicative of seal condition of the inspected seal portion; and sealcondition judgment processing means for judging from the seal conditionindicator value whether seal condition is good or defective.
 2. The sealcondition inspection apparatus of claim 1, wherein the seal conditionindicator value is the capacitance of the inspected seal portion.
 3. Theseal condition inspection apparatus of claim 1, wherein the sealcondition indicator value is the loss factor of the inspected sealportion.
 4. The seal condition inspection apparatus of claim 1, whereinthe seal condition indicator value is the capacitance and loss factor ofthe inspected seal portion.
 5. The seal condition inspection apparatusof claim 1, wherein the electrically variable quantity is voltageapplied to the inspected seal portion and current flowing through theinspected seal portion.
 6. The seal condition inspection apparatus ofclaim 5, further comprising a phase separating section for detecting, onthe basis of current flowing through the inspected seal portion, anin-phase component having the same phase as that of voltage applied tothe inspected seal portion, and an out-of-phase component having a phasedifferent from that of voltage applied to the inspected seal portion. 7.A seal condition inspection method for inspecting a seal between twosuper-imposed portions of a packaging material, the method comprising:pressing the seal with a predetermined pressure between two opposingelectrodes with the electrodes spaced apart a distance d at thepredetermined pressure, the distance d varying with seal condition;passing a current through a portion of the seal between the electrodes;detecting an electrically variable quantity of the seal portion, betweenthe opposing electrodes, as a function of distance d; calculating, onthe basis of the detected electrically variable quantity, a sealcondition indicator value, indicative of seal condition of the inspectedseal portion; and judging from the seal condition indicator valuewhether the seal condition is good or defective.
 8. The seal conditioninspection method according to claim 7 further comprising: passing afilled packaging material along a linear feed path through a sealingdevice; forming transverse seals perpendicular to the linear heat path,utilizing the sealing device and wherein the inspected seal portion is aportion of a transverse seal.